Electric valve control circuits



Sept. 2, 1941.

H. DE B. KNIGHT ELECTRIC VALVE CONTROL CIRCUITS Filed Jan. 23, 1939Fig.2.

Inventor": Henry de Bo yne Knight,

by His Attohney.

' such as boron-carbide or silicon-carbide.

Patented Sept. 2, 1941 ELECTRIC VALVE CONTROL CIRCUITS Henry de BoyneKnight, Rugby, England, assignor to General Electric Company, acorporation of New York Application January 23, 1939, Serial No. 252,469In Great Britain February 23, 1938 '7 Claims.

My invention relates to electric valve circuits, and more particularlyto control or excitation circuits for electric valve means of the typeemploying an ionizable medium and an immersionignitor control member.

In electric valve means of the type employing an immersion-ignitorcontrol member which is associated with a self-reconstructing cathode,such as a mercury pool cathode, the are between the anode and thecathode is initiated by passing through the immersion-ignitor controlmember current of predetermined magnitude. The immersion-ignitor controlmember is constructed of a suitable material having an electricalresistivity relatively large with respect to that of the associatedmercury pool cathode. The immersionignitor control member may beconstructed of a poorly conducting or semi-conducting material, Thedesign and dimensions of the ignitor control members are determined byvarious considerations. In the systems employed heretofore, the ignitorcurrent has been supplied generally from a grid controlled hot cathoderectifier, in which applications it is desirable to design the ignitorto maintain the current at a relatively low value.

This may be achieved by making the ignitor control member small indiameter at the point where it comes in contact with the cathode.Furthermore, the voltage to be applied to the ignitor should bemaintained at a low value, and for this reason the length of the controlmember should be reduced as much as possible.

On the other hand, in the case of a mercurypool type rectifier designedfor relatively large currents, additional factors come intoconsideration, as, for example, heat dissipation, mechanical forces onthe ignitor due to the movement of the mercury during transport and inoperation, and the tendency to cause changes in the mercury level and,therefore, changes in the point of contact between the ignitor and themercury, due not only to action of the cathode spot but also caused bythe evaporation of the substance of the cathode. It has been found thatthese factors necessitate an ignitor of robust design and having aminimum length.

The above stated requirements are obviously conflicting, and variousattempts have been made heretofore to produce an ignitor control memberso shaped as to compromise satisfactorily between the two sets ofconditions. Ignitors so built are, however, costly to produce anddiflicult to make with accuracy. In accordance with the teachings of myinvention described hereinafter,

I provide new and improved control systems for electric valves employingimmersion-ignitor. control members and in which the necessity for makingthe above stated compromise is obviated.

It is an object of my invention to provide new and improved electricvalve circuits.

It is another object of my invention to provide new and improvedelectric valve control circuits.

It is a further object of my invention to provide new and improvedcontrol or excitation circuits for electric valve translating apparatus.

In accordance with the illustrated embodiments of my invention, Iprovide new and improved control or excitation circuits for electricvalve means of the type employing an immersion-ignitor control member. Iemploy a main or power electric valve means having an ignitor controlmember of simple, robust design, for example, a cylindrical conductor ofsemi-conducting material long enough and sufliciently thick to copesatisfactorily with the conditions imposed on a heavy duty rectifier,but requiring a relatively high starting current. The starting currentis supplied by means of an auxiliary electric valve means of thecontrolled type having a mercury pool cathode, since this type ofelectric valve is better adapted to transmitting large peak currentsthan those of the hot cathode type. The ignition of the arc in the mainor power electric valve means is controlled by controlling the ignitionof the arc in the auxiliary electric valve means. In one embodiment ofmy invention, I provide a control electric valve or electronic dischargedevice of the thyratron type or hot cathode type which controls theenergization of the immersion-ignitor control member of the auxiliaryelectric valve. In accordance with another illustrated embodiment of myinvention, I provide an auxiliary electric valve of the type having animmersion-ignitor control member and a grid which control theenergization of the immersion-ignitor control member of the main orpower electric valve means. A source of current establishes a cathodespot on the cathode of the auxiliary electric valve during practicallythe entire positive half cycles of voltage of an associated alternatingcurrent supply circuit and the grid renders the auxiliary electric valveconductive at the desired time, thereby obtaining precise and positivecontrol of the conductivity of the power electric valve and making itpossible to supply at the precise time a relatively large startingcurrent for the power electric valve.

For a better understanding of my invention, reference may be-had to thefollowing description taken in connection with the accompanying drawing,and its scope will be pointed out in the appended claims. Figs. 1 and 2diagrammatically illustrate various embodiments of my invention asapplied to electric translating apparatus for transmitting power betweenan alternating current supply circuit and a direct current load circuit.

Referring to Fig. I of the drawing, my invention is there illustrated asapplied to electric translating apparatus for transmitting power from analternatin current supply circuit I to a direct current load circuit 2,through an electric valve means 3 which is of the type employing anionizable medium such as a gas or a vapor and which includes an anode 4,a mercury pool cathode 5, and an associated immersion-ignitor controlmember 6. The immersion-ignitor control member 6 is constructed of asemi-conducting or poorly conducting material, such as silicon carbideor boron carbide, the specific electrical resistivity of which issubstantially greater than that of the associated mercury pool cathode.The immersion-ignitor control member 6 is of robust design andconstruction, arranged to withstand substantial mechanical strain due tomechanical forces or due to the ordinary electrical operation of theelectric valve means, but requiring a sub stantially large startingcurrent.

In order to effect energization of the immersion-ignitor control member6, I provide an exciter or control circuit I which is connected betweenthe anode 4 and the cathode 5. The control circuit 1 comprises aserially connected impedance element, such as a resistance 8, and anauxiliary electric valve means or auxiliary electronic discharge device9 which is also of the type having an immersion-ignitor control memberII), a mercury pool cathode II and an anode I2. The immersion-ignitorcontrol member II) of the auxiliary electronic discharge device 9 isenergized by means of a circuit I3 which is connected across the anode I2 and the control member II] and comprises a resistance I4 and a controlelectric valve I5 of the hot cathode type having a control grid I6 whichrenders the electric valve means l5 conductive. The electric valve meansI5 is preferably of the type employing an ionizable medium. A periodicvoltage of predetermined phase displacement relative to the voltage ofthe alternating current supply circuit I is impressed on the controlgrid I6 in order to control the conductivities of the electric valvemeans 3 and 9. This periodic control voltage may be supplied from asource of alternating current II, or may be connected to the alternatingcurrent circuit I through a suitable phase shifting device such as arotary phase shifter I8. A suitable source of negative unidirectionalbiasing potential, such as a battery I9, may be employed.

The operation of the embodiment of my invention shown in Fig. 1 will beexplained by considering the system when it is designed to transmitunidirectional current to the load circuit 2. Electric valve means 3 isrendered conductive during each positive half cycle of voltage ofcircuit I to transmit direct current to the load circuit 2. The timeduring each positive half cycle of voltage at which the electric valvemeans 3 is rendered conductive is determined by the time of energizationof the immersion-ignitor control member 6. The auxiliary electronicdischarge device 9 conducts unidirectional current to the control member6 from the supply circuit I at the desired time to render the electricvalve means 3 conductive. The electronic discharge device 9 in turn isrendered conductive by the control electric valve means I5 which in turnis controlled by the rotary phase shifter I8. Since the electronicdischarge device 9 is of the mercury pool cathode type, a relativelylarge starting current is transmitted to the control member 6 in orderto assure positive and accurate starting of the electric valve means 3.Of course, as soon as the electric valve means 3 is rendered conductive,the voltage appearing across the anode and cathode thereof decays sothat current is no longer transmitted to the control member 6.

Fig. 2 diagrammatically illustrates another embodiment of my inventionwhich is similar in many respects to that shown in Fig. 1, andcorresponding elements have been assigned like reference numerals. Inthe embodiment of my invention shown in Fig. 2 I provide an auxiliaryelectric valve means or electronic discharge device 20 which ispreferably of the type employing an ionizable medium, such as a gas or avapor, and is particularly illustrated as employing mercury vapor as theionizable medium. The auxiliary electronic discharge device 20 comprisesan anode 2|, a mercury pool cathode 22, an immersion-ignitor controlmember 23 and a control grid 24. The electronic discharge device 20 isconnected across the anode 4 and the control member 6 of the electricvalve means 3 and transmits relatively large amounts of unidirectionalcurrent to the control member 6 from the alternating current circuit Iin order to render the electric valve means 3 conductive. A suitablecurrent limiting or controlling impedance, such as a resistance 25, maybe connected in series relation with the electronic discharge device 20.The control member 23 of the electronic discharge device 20 maintains acathode spot on the cathode 22 so long as the control member 23 isproperly energized and the control grid 24 renders the electric valvemeans conducting, that is, establishes an arc discharge between theanode 2| and the cathode 22, thereby effecting precise and accuratecontrol of the time at which theteleotronic discharge device 29 conductscurren As a means for supplyin current to the control member 23 in orderto maintain a cathode spot on cathode 22, I provide a control circuitwhich may comprise a transformer 26, a unidirectional conducting device27 and a current limiting resistance 28. The circuit transmits asubstantially unidirectional current to the control member 23 and thatcurrent may be controlled so that the cathode spot is maintained duringsubstantially the entire positive half cycles of voltage of circuit I.The time during which the cathode spot is maintained may be controlledby means of a rotary phase shifting device 29 which is energized from asuitable source of alternating current 30. Of course, the rotary phaseshifter 29 tmay be connected to alternating current circui In operationthe rotary phase shifter 23 is adjusted in order that a cathode spot ismaintained on the cathode 22 during substantially the entire positivehalf cycles of voltage of circuit I. Of course, the electric valve means3 will not be rendered conductive until current is transmitted to thecontrol member 6 by the electronic discharge device 20. The electronicdischarge device 20 will not conduct current until a suitable voltage isimpressed on the control grid 24 by means or the rotary phase shifterl8. By the proper positioning of the rotary phase shifter IS, the timesduring the positive cycles of the voltage of circuit I at which theelectronic discharge means 20 is rendered conductive, are controlled tocontrol the amount of current transmitted by the electric valve means 3.The control circuit transmits only unidirectional current to theimmersion-ignitor control member 23. The circuit including thetransformer 26, unidirectional conducting device 21 and the phaseshifter 29 transmits to the control member 23 a series or train ofdiscrete impulses of unidirectional current which are correlated in timerelationship with respect to the voltage of the alternating currentcircuit I. These impulses are transmitted to the control member duringalternatev half cycles of voltage of circuit I. Since the cathode spotis maintained on the cathode 22 during substantially the entire positivehalf cycles of voltage of circuit I or for a predetermined interval oftime prior to the time at which it is desired to render the electronicdischarge device 20 conductive, the electronic discharge device 20 maybe rendered conductive at precise times and a sufliciently largestarting current may be transmitted to the immersion-ignitor controlmember 6 of the power electric valve means 3, thereby permitting the useof a rugged and substan tial construction of the immersion-ignitorcontrol member 6.

While I have shown and described my invention as applied to a particularsystem of connections and as embodying various devices diagrammaticallyshown, it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention, and I,therefore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an alternating current circuit, a load circuit,electric valve means connected between said circuits and comprising ananode, a cathode and a control member of the immersion-ignitor type, anexcitation circuit for energizing said control member connected betweensail anode and said control member and comprising an electric valvemeans including an anode, a cathode and an immersion-ignitor controlmember, means for energizing said second mentioned control membercomprising means for transmitting to said control member discreteimpulses of unidirectional current to maintain a cathode spot on saidsecond mentioned cathode during substantially the entire positive halfcycle of voltage of said alternating current circuit, and means forcontrolling the conductivity of said second mentioned electric valvemeans to effect energization of said first mentioned control member.

2. In combination, an alternating current supply circuit, a loadcircuit, electric valve means connected between said circuits andincluding an immersion-ignitor control member, an excitation circuit forenergizing said control member and including an auxiliary electronicdischarge device for energizing said control member and including ananode, a cathode, animmersion-ignitor control member and a control grid,means including a rectifier for transmitting discrete impulses ofunidirectional current to said control member for maintaining a'cathodespot on said cathode during substantially the entire positive halfcycles of voltage of said alternating current circuit, and means'forenergizing said grid to render said electronic discharge deviceconducting to efiect energization of said first mentioned controlmember.

3. In combination, an'alternating current supply circuit, a loadcircuit, electric valve means connected between said circuitsandincluding an immersion-ignitor control member, an excitation circuit forenergizing said control member and including an auxiliary electronicdischarge device for energizing said control member and including ananode, a cathode, an immersion-ignitor control member and a controlgrid, means for energizing said control member comprising a source ofcurrent for energizing said second mentioned immersion-ignitor controlmember and a unidirectional conducting device for transmitting to saidcontrol member discrete impulses of unidirectional current to maintain acathode spot on said cathode during substantially the entire positivehalf cycles of voltage of said source, and means for impressing on saidgrid a periodic voltage to render said electronic discharge deviceconducting at predetermined times during the cycles of voltage of saidalternating current circuit.

4. In combination, an alternating current circuit, a load circuit,electric valve means connected between said circuits and including animmersion-ignitor control member, an excitation circuit for energizingsaid control member and including an auxiliary electronic dischargedevice for energizing said control member and including an anode, acathode, an immersion-ignitor control member and a control grid, meansfor supplying discrete impulses of unidirectional current to said secondmentioned control member to maintain a cathode spot on the associatedcathode during substantially the entire half cycles of voltage of saidalternating current circuit, and means for energizing said grid torender said electronic discharge device conducting.

5. In combination, an alternating current circuit, a second circuit,electric translating apparatus connecting said circuits and comprisingan electronic discharge device including an anode, a cathode, animmersion-ignitor control member associated with said cathode and acontrol grid, means for supplying to said control member discreteimpulses of unidirectional current timed with respect to the voltage ofsaid alternating current circuit to establish a cathode spot on saidcathode during each cycle of the voltage of said alternating currentcircuit, means for impressing a potential on said control grid tomaintain said discharge device nonconducting, and means for modifyingsaid potential to permit the flow of current between said anode and saidcathode.

6. In combination, an alternating current circuit, a second circuit,electric translating apparatus connected between said circuits forcontrolling the transfer of power therebetween and including an electricdischarge device of the type employing an ionizable medium andcomprising an anode, a cathode, an immersion-ignitor control member anda control grid, means for energizing said control member comprisingmeans for transmitting to said control member a series of discreteimpulses of unidirectional current timed with respect to the voltage ofsaid alteran anode, a cathode, an immersion-ignitor control memberassociated with said cathode and a control grid, means for transmittingcurrent to said control member during alternate half cycles of voltageof said alternating current circuit to establish a cathode spot on saidcathode during each cycle of the voltage of said alternating currentcircuit, means for impressing a potential on said control grid tendingto maintain said discharge device nonconducting, and means for modifyingsaid potential to initiate the flow of our- 10 rent between said anodeand said cathode.

HENRY DE BOYNE KNIGHT.

